Method for producing green salt (UF4) from uranium and uranium alloy pieces

ABSTRACT

A method and apparatus are provided for producing green salt (UF 4 ) from uranium-bearing metal pieces. The uranium-bearing metal pieces are dissolved in a first aqueous solution containing hydrochloric acid and between 0.5% and 5% fluoboric acid to provide a second aqueous solution which includes uranium (U +4 ), chlorine ions (Cl - ) and hydrochloric and fluoboric acids. Hydrofluoric acid is added to the second aqueous solution to precipitate green salt out of that solution and provide a third aqueous solution which contains hydrochloric acid. The green salt is then separated from the third aqueous solution.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in part of U.S. patent applicationSer. No. 723,302 filed Apr. 15, 1985, now U.S. Pat. No. 4,699,769.

FIELD OF INVENTION

This invention relates to a method and apparatus for producing greensalt (UF₄) from uranium and uranium-bearing metal pieces and to a greensalt (UF₄) product produced according to that method.

BACKGROUND OF INVENTION

It is presently difficult and expensive to dispose of uranium anduranium alloy (e.g., uranium-titanium, uranium-molybdenum) chipsobtained from machining operations. The chips must first be cleaned anddried. Water must be totally removed because water reacts with theuranium leaving hydrogen (H₂) which presents an explosive hazard. Theuranium and uranium alloy chips may then be compacted into discs toreduce volume and exposed surface area of the chips to oxidation. Groupsof these discs are encapsulated in copper cans and crushed again. Thecopper can encloses the uranium further limiting the surface area of theuranium to oxidation. These crushed copper cans are then buried indesignated waste sites.

The above disposal procedures are complex and expensive. Moreover,approximately 50% of the uranium material present at the beginning ofthe machining operation is buried and lost. Valuable resources aretherefore wasted.

SUMMARY OF INVENTION

It is therefore an object of this invention to provide a method andapparatus for producing green salt (UF₄) from uranium anduranium-bearing metal pieces which enables uranium to be retrieved forreuse from waste metals and machine scraps.

It is a further object of this invention to provide a method andapparatus for producing green salt which enables valuable uranium to beused more efficiently and completely and which reduces the expense,waste, and inconvenience associated with the conventional disposal ofuranium and uranium alloy waste.

It is a further object of this invention to provide a quick, inexpensiveand effective method for recycling uranium-bearing metal pieces whicheliminates the need for crushing and drying those pieces.

It is a further object of this invention to provide a method forproducing green salt which uses fluoboric acid as a catalyst to dissolveuranium and limit the amount of sludge formed.

It is a further object of this invention to provide a method andapparatus for producing green salt from uranium-bearing metal pieceswhich employs a relatively dilute acid.

It is a further object of this invention to provide a method andapparatus for effectively removing metal impurities from uranium anduranium alloy pieces.

It is a further object of this invention to provide a high purity greensalt product produced according to the method of this invention.

This invention features a method of producing green salt (UF₄) fromuranium-bearing metal pieces which includes dissolving theuranium-bearing metal pieces in a first aqueous solution containinghydrochloric acid and fluoboric acid with a concentration of at least0.5% but no more than 5.0% to provide a second aqueous solution whichincludes uranium (U₊₄), chloride ions (Cl⁻) and hydrochloric andfluoboric acids. Hydrofluoric acid (HF) is added to the second aqueoussolution to precipitate green salt out of the second solution andprovide a third aqueous solution containing hydrochloric acid. The greensalt is then separated from the third aqueous solution.

In a preferred embodiment the first aqueous solution may include aconcentration of at least 0.5% but no more than 2% fluoboric acid.Although dissolution of the uranium pieces may be accomplished withhydrochloric acid concentration of 50% or more, the first aqueoussolution preferably includes no more than a 25% concentration ofhydrochloric acid. Insoluble materials in the second solution may beremoved and hydrogen gas released as the uranium-bearing metal piecesare dissolved in the first solution may be removed from the containerthrough a vent.

An aqueous solution of hydrofluoric acid may be added to the secondaqueous solution to precipitate green salt (UF₄) out of the secondsolution and provide a third aqueous solution containing at leasthydrochloric acid. Alternatively, gaseous hydrofluoric acid may beadded. To assist with the precipitation the hydrofluoric acid may bestirred into the second solution. The green salt precipitate may beseparated by centrifuging or by filtering.

Following the separation of the green salt precipitate from the thirdaqueous solution the precipitate may be washed and dried for furtherreprocessing. The third aqueous solution may be analyzed for acidcontent and water, hydrochloric acid, and/or fluoboric acid may be addedto the third aqueous solution. The third aqueous solution containinghydrochloric acid may be used as at least a portion of the first aqueoussolution to dissolve successive uranium-bearing metal pieces.

This invention also features a green salt product produced according tothe method of this invention. Further featured is an apparatus forproducing green salt from uranium-bearing metal pieces. There are firstcontainer means for dissolving uranium-bearing metal pieces in a firstaqueous solution which includes hydrochloric acid and fluoboric acid inthe above concentration to provide a second aqueous solution whichincludes uranium (U⁺⁴), chloride ions and hydrochloric and fluoboricacids. The container means also receives hydrofluoric acid toprecipitate green salt out of the second solution and provide a thirdsolution which includes hydrochloric and fluoboric acids. There areseparator means connected to the first container means through a firstconduit means for receiving the precipitate and the third solution andseparating the precipitate from the third solution. Second containermeans are connected to the separator means through second conduit meansfor receiving third solution from the separator means. Third conduitmeans are connected between the second container means and the firstcontainer means and there are means for moving the third aqueoussolution through the third conduit means from the second container meansto the first container means to reintroduce the third solution in thefirst solution.

Preferably, the apparatus also includes means for removing sludge fromthe first container means. Vent means may be provided for drawinghydrogen gas from the vicinity of the first container. Second means maybe provided for moving the third solution through the first conduitmeans. There may be means communicably connected with the separatormeans for receiving green salt therefrom. The first container means mayinclude a reaction tank and the separator means may include a filterpress.

DISCLOSURE OF PREFERRED EMBODIMENT

Other objects, features and advantages will occur from the followingdescription of the preferred embodiment and the accompanying drawings,in which:

FIG. 1 is a diagram of a method for producing green salt fromuranium-bearing metal pieces according to this invention; and

FIG. 2 is an elevational, partly schematic view of an apparatus forproducing green salt from uranium-bearing metal pieces according to thisinvention.

A method and apparatus for producing green salt (uranium tetrafluoride)from uranium-bearing metal pieces according to this invention may beaccomplished by dissolving pieces of uranium or uranium alloy in a firstcontainer holding a first aqueous solution which includes typically 25%or less hydrochloric acid. The pieces are usually chips, scraps, orfines formed form the machining or grinding of uranium or uranium alloyssuch as U-Ti or U-Mo. Such pieces can be dissolved rapidly inhydrochloric acid having concentration of 35% or stronger. However, suchhigh concentrations make the dissolution difficult to control due to theexothermic nature of the reaction. Additionally, approximately 20% ofthe metal produces a sludge (such as hydrated uranium oxide) whichcannot be dissolved without the addition of an oxodizing agent such asnitric acid (HNO₃). The use of such an agent produces an undesireduranyl ion (UO₂ ²⁺) which does not permit the formation of green salt.

Accordingly, a small concentration (e.g., at least 0.5% but no more than5%) of fluoboric acid (HBF₄) is included in the first aqueous solution.The fluoboric acid limits the formation of the undesirable sludge andacts as a catalyst to permit the rapid and controlled dissolution of themetal or metal alloy with a more dilute, e.g., 10%, concentration ofhydrochloric acid. Enhanced control over the dissolution of theuranium-bearing metal pieces is thereby achieved. In contrast, it wasdisclosed in the parent application, Ser. No. 723,302, that theconcentration of fluoboric acid should be limited to no greater than2.0%. The pieces dissolve into a second aqueous solution which includesuranium (U⁺⁴), chloride ions (Cl⁻), hydrochloric acid, and fluoboricacid. Alloy metals such as titanium or molybdenum, if present, are alsodissolved in the second solution. Insoluble materials such as refractoryoxides drop to the bottom of the first container and may be eliminatedby bottom draining or coarse filtration. One such apparatus forperforming such removal is the JWI Filter Press Model 470. Thedissolution of the uranium-bearing pieces also liberates hydrogen (H₂)which is vented from the vicinity of the container.

Hydrofluoric acid (HF) either in aqueous solution or gaseous form isadded to the second aqueous solution and green salt (UF₄) is thereforeprecipitated out of that solution. To encourage such precipitation thehydrofluoric acid may be stirred into the second solution. A thirdaqueous solution containing hydrochloric and fluoboric acids is therebyprovided and that solution and the green salt precipitate it containsare moved, typically through a conduit to separator means for separatingthe green salt from the third aqueous solution. The third aqueoussolution is then delivered to a second container through a secondconduit wherein the acid content of the third aqueous solution may beanalyzed. Water, hydrochloric acid and/or fluoboric acid may be added tothe third aqueous solution to bring those constituents to approximatelythe level of the first aqueous solution. The third aqueous solution,which also includes any metals such as titanium or molybdenum dissolvedin the first container, is moved as required through a third conduitfrom the second container back to the first container where it may beutilized as, or in combination with, the first aqueous solution todissolve successive loads of uranium-bearing metal pieces.

The green salt is washed with water to reduce impurities and is at leastpartially dried. It may then be removed from the separator means andstored in drums or similar containers. Eventually, the green salt may befurther dried and employed in magnesium reduction processing to makeuranium (metal derby).

The first container may include a reaction tank. A preferred acceptabletank is made by Perry Products Corp. The separator means may include apress filter such as the JWI Filter Press Model 470, a centrifuge orother such solids/liquid separation apparatus. Typically the secondcontainer is a filtrate tank such as that manufactured by Perry ProductsCorp. Conventional pumps may be employed to move the solutions betweenthe containers and separator means.

The following example is provided to illustrate the quantities ofmaterials and chemicals and the times which may be employed in theprocess of this invention. These values, however, are provided forillustrative purposes only. The process of this invention is limitedonly by the claims.

The first aqueous solution may include 90 gallons of water, 10 gallonsof hydrochloric acid and 0.6 gallons of fluoboric acid. To this solution100 lbs. of oil-free uranium and/or uranium alloy scrap may be added ata rate which limits the exothermic reaction temperature to 160° F. Thepieces are added until dissolution is complete. Seven gallons ofhydrofluoric acid, having a concentration of 49% may then be added tothe second aqueous solution. The solution is stirred for an hour untilthe green salt (UF₄) has completely precipitated out of solution. Afterseparation of green salt from the third aqueous solution that solutionis analyzed for losses in hydrochloric acid and water. The requiredamount of each is added to bring the solution to a level of 100 gallonsand a 10% concentration of hydrochloric acid. The solution may then berecycled for use in dissolving an additional 100 lbs. of uranium and/oruranium alloy scrap. Recycling may be continued until metal impurities(e.g., Fe, Ni, Cu, Si, Ti and Mo) reach undesirably high levels. Thoselevels may vary according to the intended uses for the recycled greensalt. A small amount of the first solution maybe disposed of before itis recycled to maintain the impurity level within the desired limits.

There is shown in FIG. 1 a method for producing green salt fromuranium-bearing metal chips according to this invention. Machined andlubricated uranium, and/or uranium alloy pieces are introduced into acentrifuge 10 where they are washed in water to remove the lubricant andthen centrifuged to remove excess water. The oil-free pieces are thenintroduced into a first container 12 which contains an aqueous solution13 of hydrochloric acid (HCl) having a concentration of 10% or less andfluoboric acid (HBF₄) having a concentration of 0.5 to 1%. Theconcentration of fluoboric acid may be selectively increased to as highas 5.0%. The pieces are dissolved in solution 13 to provide a secondaqueous solution 14 according to the following equation: ##STR1##

Aqueous solution 14 includes water, hydrochloric and fluoboric acids,uranium (U⁺⁴) and chloride ions (Cl⁻). It also includes dissolved alloymetals such as titanium and molybdenum present in the metal pieces.Hydrogen gas H₂ is liberated by the reaction. Insoluble oxides may beremoved from the bottom of container 12. The presence of fluoboric acidprevents the formation of sludge and catalyzes the reaction.

Hydrofluoric acid (HF) is then added to solution 14 within container 12.The hydrofluoric acid reacts with the second solution 14 according tothe following formula:

    U.sup.4+ +4 Cl.sup.- +4HF→UF.sub.4 ↓+4HCl

This reaction may be encouraged by stirring the hydrofluoric acid for upto an hour. Green salt (UF₄) 17 is therefore precipitated out ofsolution 14 to provide a third aqueous solution 16. The green salt 17and solution 16 are then delivered as indicated by arrow 18 to separator20 wherein the green salt is separated from solution 16. Any U⁺⁴ and Cl⁻remaining in the solution are separated and returned to container 12.Solution 16 is delivered to a second container 22 where its acid andwater content are analyzed. The free acid level is typically determinedby titration with a standard base (e.g., 0.5 NaOH). The water level isdetermined by total volume in container 22. Acid and water may be addedto bring their respective levels to those of aqueous solution 11. Asolution 24 is thereby provided which includes each of the constituentsand concentrations of solution 11 with the possible addition ofdissolved metal impurities (e.g., titanium, molybdenum).

Following separation of the green salt from third solution 16 the greensalt may be washed with water in the separator 20 to reduce impuritiessuch as Cu, Ni, Fe, Si, Ti, and Mo. The green salt is then partiallydried by back-flushing with air and is removed from separator 20 andstored as at 26. Subsequently the green salt may be dried further at 28and subjected to the magnesium reduction process 30 to provide recycleduranium (metal derby) 32.

An apparatus for accomplishing the method of this invention is shownmore clearly in FIG. 2. Aqueous solution 11, including hydrochloric andfluoboric acid, and uranium-bearing pieces P are introduced into areaction tank 12a and pieces P are dissolved in solution 11. Refractoryoxides or other undesirable insoluble materials dropped to the bottom oftank 12a and are drained or filtered by filter 30. Hydrogen H₂ gas isalso liberated by the reaction and vented from the vicinity of tank 12by hood 32.

Hydrofluoric acid (HF) is added to the solution in tank 12a therebycausing green salt UF₄ to precipitate out of the solution. An aqueoussolution including hydrochloric and fluoboric acids and green saltprecipitate are pumped by pump 36 through a conduit 38 in the directionof arrow 40 to a filter press 20a. There the aqueous solution isseparated from the green salt. The green salt may be washed and dried infilter press 20a and then deposited in a storage container 50. UraniumU⁴⁺ and chloride ions (Cl⁻) remaining in the solution are also separatedby press 20a and returned to container 12a via conduit 51.

The aqueous solution 16 is delivered by conduit 52 in the direction ofarrow 53 to a filtrate tank 22a. The acid level of the filtrate (e.g.,the aqueous solution in tank 22a) is analyzed and water and/or acid areadded to bring their levels to those of the first aqueous solution 11.Filtered solution 24 is then pumped as needed by a pump 60 throughconduit 62 back to reaction tank 12a where it may be employed todissolve subsequent batches of uranium-bearing pieces.

The apparatus disclosed is only one example of an apparatus which may beused to practice this invention. This invention is not limited to theillustrated apparatus and may be practiced on various alternativeapparatuses.

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

What is claimed is:
 1. A method of producing green salt (UF₄) fromuranium-bearing metal pieces comprising:dissolving the uranium-bearingmetal pieces in a first aqueous solution containing hydrochloric acidand at least 0.5% but no more than 5.0% fluoboric acid to provide asecond aqueous solution which includes uranium (U⁺⁴), chloride ions andhydrochloric and fluoboric acids; adding hydrofluoric acid to saidsecond aqueous solution to precipitate green salt out of said secondsolution and provide a third aqueous solution containing hydrochloricacid; and separating said green salt from said third aqueous solution.2. The method of claim 1 in which said first aqueous solution includesno more than 50% hydrochloric acid.
 3. The method of claim 1 in whichsaid first aqueous solution includes no more than 25% hydrochloric acid.4. The method of claim 1 in which an aqueous solution of hydrofluoricacid is added to said second aqueous solution.
 5. The method of claim 1in which gaseous hydrofluoric acid is added to said second aqueoussolution.
 6. The method of claim 1 in which said green salt precipitateis separated by centrifuging.
 7. The method of claim 1 in which saidgreen salt precipitate is separated by filtering.
 8. The method of claim1 in which said hydrofluoric acid is stirred into said second solution.9. The method of claim 1 further including washing said green saltprecipitate following its separation from said third aqueous solution.10. The method of claim 9 further including drying said washed greensalt precipitate.
 11. The method of claim 1 further including using saidthird aqueous solution containing hydrochloric acid as at least aportion of said first aqueous solution to dissolve successiveuranium-bearing metal pieces.
 12. The method of claim 1 furtherincluding analyzing the acid content of said third aqueous solution. 13.The method of claim 11 further including adding water to said thirdaqueous solution following separation of said green salt and using saidthird solution in said first solution to dissolve successiveuranium-bearing metal pieces.
 14. The method of claim 11 furtherincluding adding hydrochloric acid to said third aqueous solution. 15.The method of claim 11 further including adding fluoboric acid to saidthird aqueous solution following separation of said green salt and usingsaid third solution in said first solution to dissolve successiveuranium-bearing metal pieces.
 16. The method of claim 1 furtherincluding removing insoluble materials from said second aqueoussolution.
 17. The method of claim 1 further including venting hydrogengas released as the uranium-bearing metal pieces are dissolved in thefirst solution.
 18. A method of producing green salt (UF₄) fromuranium-bearing metal pieces comprising:dissolving said uranium-bearingmetal pieces in a first aqueous solution containing hydrochloric acidand at least 0.5% but no more than 5.0% fluoboric acid to provide asecond aqueous solution containing uranium (u⁺⁴), chloride ions andhydrochloric and fluoboric acids; removing insoluble materials from saidsecond solution; adding hydrofluoric acid to said second solution toprecipitate green salt out of said second aqueous solution and provide athird aqueous solution containing hydrochloric and fluoboric acids; andseparating said green salt from said third aqueous solution.